1. Field of the Invention
The present invention relates to an oil separator for a blowby gas containing oil mist, and particularly relates to a novel structure of an oil separator for a blowby gas containing oil mist to separate the oil mist contained in the blowby gas generated inside an internal combustion engine.
2. Discussion of Related Art
As is well known, in an internal combustion engine, such as an engine of a car, at the time of operating the engine, a blowby gas containing a large amount of unburned hydrocarbons inevitably leaks out from gaps between piston rings and cylinder walls to an inside of a crankcase. As a result, in this type of vehicle engine, the blowby gas is often forcibly flowed inside an intake pipeline utilizing negative pressure inside the intake pipeline, returned once more to the combustion chamber, and combusted again.
Meanwhile, an oil mist, that is a lubricating oil such as an engine oil made into a mist state and dispersed, is also contained within the blowby gas. Therefore, conventionally, for the purpose of reducing an amount of oil carried away due to commingling of the oil with the blowby gas, and preventing pollution due to the oil in the intake pipeline, an oil separator for separating the oil mist from within the blowby gas has been provided in various configurations, such as at an inner side of a cylinder head cover, and at a mid point of a connecting passage connecting a crankcase and the intake pipeline.
As this type of oil separator, is known, for example, as an oil separator comprising: a gas flow passage for allowing the flow of the blowby gas from a gas inlet port towards a gas outlet port; a separation mechanism, provided midway along the gas flow passage, for separating the oil (oil in the form of mist) from within the blowby gas flowing inside the gas flow passage; an oil passage, having at least a part shared with a part of the gas flow passage that is located downstream of the separation mechanism, in the blowby gas flowing direction, for causing the oil that has been separated (oil that has been separated, condensed and formed into droplets) to flow along a bottom positioned below; and an oil discharge port, provided at a downstream side end section, in the oil flowing direction, of the oil passage, for discharging the oil (oil in the form of droplets) flowing inside the oil passage to the outside of the oil passage, as disclosed in, for example, JP-A-2000-45750. A similar oil separator is also disclosed in JP-A-2004-204811.
In an oil separator having this type of configuration, in the separation mechanism, the oil that has been separated from the blowby gas and formed into the droplets is not accumulated inside the common flow path section formed as a common section to the oil passage and the gas flow passage, but instead swept away towards the oil discharge port side by the flow of the blowby gas on a bottom of the common flow path section so as to be discharged reliably from the oil discharge port to the outside of the oil passage.
However, after investigation by the present inventors with respect to oil flow that stays inside the conventional oil separators as described above, it has been established that there are cases where if there is a large amount of the blowby gas flowing inside the gas flow passage and the flow rate increases, the oil that is separated in the separation mechanism and formed into the droplets is largely blown off the inside of the common flow path section by the blowby gas, and thereby dispersed again or made to flow in an entrained manner, so that some of the oil is not discharged from the oil discharge port but carried away by the blowby gas and discharged together with the blowby gas from the gas exhaust outlet. That is, with the conventional oil separator, it is understood that there may be caused variations in separation characteristics of the oil depending on intake amount of the blowby gas.